cdefs: Remove vararg related defines, they are unused.

Remove GNUCLIKE_BUILTIN_VARARGS, GNUCLIKE_BUILTIN_STDARG,
GNUCLIKE_BUILTIN_VAALIST, GNUC_VA_LIST_COMPATIBILITY: they are
unused. Also remove them from the generated cryptodevh.py script.

PR: 275221 (exp-run)
Sponsored by: Netflix